For example, a pressure sensor that is widely used is comprised of a diaphragm formed over a portion of a semiconductor chip and a piezoresistive element arranged in a bridge shape on the diaphragm, and pressure on a medium to be measured is sensed by converting the displacement of the diaphragm, corresponding to the pressure on the medium to be measured, into a change in resistance of the piezoresistive element (see Japanese Unexamined Patent Application Publication No. 2002-277337 (page 2, FIG. 2), for example).
Moreover, inventions relating to a process for manufacturing pressure sensors by forming a diaphragm on a semiconductor chip while rigorously controlling the thickness of this type of diaphragm are also known (see Japanese Unexamined Patent Application Publication No. 2000-171318 (pages 3-4, FIG. 1), for example).
Silicon has typically been used as the semiconductor chip material for pressure sensors, but in considering a semiconductor material such as silicon in its agglomerate state, the physical properties of this semiconductor material, i.e., the degree of deformation (strain) in response to an external force, namely, the stress-strain characteristic, exhibits near linearity, and almost no non-linearity. In other words, this physical property arises when the semiconductor material is considered to be in its agglomerate state. However, in the case where silicon or other semiconductor material, having been controlled precisely in a crystalline state, is processed to become thinner beyond a certain extent, that there will be an increase in non-linearity is understood qualitatively.
However, this attribute of increased non-linearity is only known in a qualitative sense, and in a pressure sensor comprised of a diaphragm formed over a portion of a chip comprised from this type of semiconductor material, wherein pressure is sensed by electrically converting the displacement that corresponds to a pressure acting on the diaphragm, the specific range of dimensions within which to reduce the thickness of the diaphragm so as to satisfy divergent requirements for expanding the non-linear range of the stress-strain characteristic and providing high sensitivity with high pressure resistance is still unclear.
In other words, in a pressure sensor chip having a pressure-sensitive diaphragm portion, the stress generated at the diaphragm constitutes the sensor sensitivity, and therefore, in order to provide the pressure sensor with high sensitivity and high pressure resistance, the dimensional parameters of the pressure sensor diaphragm must be controlled specially to expand the non-linear region to the extent possible so as to satisfy the divergent requirements. By specifically discovering these types of dimensional parameters, it was hoped that the divergent requirements for high sensitivity and high pressure resistance could be satisfied and that the limiting range of pressure sensors could be expanded.
An object of the present invention is to provide a pressure sensor that has high sensitivity and high pressure resistance.